It has been reported that the compound of the formula (1) has a superior agonistic activity to an arginine vasopressin V2 receptor and is useful as an active ingredient of a pharmaceutical composition for preventing and/or treating urinary frequency, urinary incontinence, enuresis, central diabetes insipidus, nocturia, nocturnal enuresis, or the like (Patent Document 1).

In reference to reference examples and examples described in Patent Document 1, the method for producing a compound of the formula (1) (Example 55) described therein is found to be those shown in the reaction scheme (I).
Further, with regard to a method for producing a compound of the formula (8-M) from a compound of the formula (16) through the steps 10 to 15 shown in the reaction scheme (I), the method is specifically described in Non-Patent Document 1.

(in the formula, Ts represents p-toluenesulfonyl, Bn represents benzyl, Ac represents acetyl, Me represents methyl, DAST represents (diethylamino)sulfur trifluoride, and EDC represents 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride).
However, the method for producing a compound of the formula (1) disclosed in Patent Document 1 requires a large number of steps, that is, eighteen steps in total, and includes, for example, a step with a low yield of products as described later, such as a step with a yield of about 30% or less, and thus, the overall yield from the compound of the formula (16) to the compound of the formula (1) as a final target is about 6%. In this regard, since the method has a big challenge in a yield and cost, from an industrial point of view, it was not entirely satisfactory production methods. In addition, the production method still needs to be further improved in terms of industrial production of a medicament from the viewpoint that the method includes a step (i.e. step 8 in the reaction scheme (I)) using (diethylamino)sulfur trifluoride (DAST) which is a nucleophilic fluorinating agent that is not easily handled due to its toxicity, corrosiveness, explosion hazard during a reaction, or the like, a step (i.e. step 18 in the reaction scheme (I)) using 1-ethyl-3-(3-dimethylaminopropyl)carbodiimide hydrochloride (EDC) which exhibits mutagenicity, and steps (i.e. steps 1, 2, 7, and 8 in the reaction scheme (I)) requiring purification by column chromatography.